Liquid crystal display devices are used in applications such as watches, calculators, measuring instruments, automotive instrument panels, word processors, electronic organizers, printers, computers, televisions, clocks, and advertisement boards. Typical liquid crystal display modes include twisted nematic (TN), super-twisted nematic (STN), and other modes based on thin-film transistors (TFTs), such as VA, which is characterized by vertical alignment, and in-plane switching (IPS)/FFS, which is characterized by horizontal alignment. Liquid crystal compositions used in liquid crystal display devices are required to be stable to external factors such as moisture, air, heat, and light, to exhibit a liquid crystal phase over a wider temperature range centered on room temperature, and to have low viscosity and low driving voltage. In addition, liquid crystal compositions are composed of several to tens of compounds to optimize properties such as dielectric anisotropy (Δε) and refractive index anisotropy (Δn) depending on the specific display device.
Whereas liquid crystal compositions of negative Δε are used in vertical-alignment displays, liquid crystal compositions of positive Δε are used in horizontal-alignment displays such as TN, STN, and IPS displays. Recently, a driving mode has been reported in which a liquid crystal composition of positive Δε is vertically aligned when no voltage is applied and is driven by applying an IPS/FFS electric field, boosting the need for liquid crystal compositions of positive Δε. Liquid crystal compositions are also required to have low driving voltage, high response speed, and a wide operating temperature range in all driving modes. Specifically, liquid crystal compositions are required to have a positive Δε large in absolute value, a low viscosity (η), and a high nematic phase-isotropic liquid phase transition temperature (Tni). The Δn of liquid crystal compositions also needs to be adjusted to an appropriate range depending on the cell gap by taking into account the product of Δn and the cell gap (d), i.e., Δn×d. Liquid crystal compositions used in applications such as televisions are also required to have a low γ1 since quick response is of a higher priority in these applications.
There are disclosed liquid crystal compositions containing compounds represented by formulas (A-1) and (A-2), which are liquid crystal compounds of positive Δε (PTLs 1 to 4). These liquid crystal compositions, however, fail to provide sufficiently low viscosity. Also disclosed are compounds represented by general formulas (A-3) and (A-4), which have a —CF2O— or —OCF2— linking group, and liquid crystal compositions containing such compounds (PTLs 5 to 21). Again, these liquid crystal compositions fail to provide sufficiently low viscosity.
